1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
|
/*
* Copyright (C) 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <sched.h>
#include <condition_variable>
#include <mutex>
#include <thread>
template <typename Impl>
class StreamWorker {
enum class WorkerState { STOPPED, RUNNING, PAUSE_REQUESTED, PAUSED, RESUME_REQUESTED, ERROR };
public:
StreamWorker() = default;
~StreamWorker() { stop(); }
bool start() {
mWorker = std::thread(&StreamWorker::workerThread, this);
std::unique_lock<std::mutex> lock(mWorkerLock);
mWorkerCv.wait(lock, [&] { return mWorkerState != WorkerState::STOPPED; });
return mWorkerState == WorkerState::RUNNING;
}
void pause() { switchWorkerStateSync(WorkerState::RUNNING, WorkerState::PAUSE_REQUESTED); }
void resume() { switchWorkerStateSync(WorkerState::PAUSED, WorkerState::RESUME_REQUESTED); }
bool hasError() {
std::lock_guard<std::mutex> lock(mWorkerLock);
return mWorkerState == WorkerState::ERROR;
}
void stop() {
{
std::lock_guard<std::mutex> lock(mWorkerLock);
if (mWorkerState == WorkerState::STOPPED) return;
mWorkerState = WorkerState::STOPPED;
}
if (mWorker.joinable()) {
mWorker.join();
}
}
bool waitForAtLeastOneCycle() {
WorkerState newState;
switchWorkerStateSync(WorkerState::RUNNING, WorkerState::PAUSE_REQUESTED, &newState);
if (newState != WorkerState::PAUSED) return false;
switchWorkerStateSync(newState, WorkerState::RESUME_REQUESTED, &newState);
return newState == WorkerState::RUNNING;
}
// Methods that need to be provided by subclasses:
//
// Called once at the beginning of the thread loop. Must return
// 'true' to enter the thread loop, otherwise the thread loop
// exits and the worker switches into the 'error' state.
// bool workerInit();
//
// Called for each thread loop unless the thread is in 'paused' state.
// Must return 'true' to continue running, otherwise the thread loop
// exits and the worker switches into the 'error' state.
// bool workerCycle();
private:
void switchWorkerStateSync(WorkerState oldState, WorkerState newState,
WorkerState* finalState = nullptr) {
std::unique_lock<std::mutex> lock(mWorkerLock);
if (mWorkerState != oldState) {
if (finalState) *finalState = mWorkerState;
return;
}
mWorkerState = newState;
mWorkerCv.wait(lock, [&] { return mWorkerState != newState; });
if (finalState) *finalState = mWorkerState;
}
void workerThread() {
bool success = static_cast<Impl*>(this)->workerInit();
{
std::lock_guard<std::mutex> lock(mWorkerLock);
mWorkerState = success ? WorkerState::RUNNING : WorkerState::ERROR;
}
mWorkerCv.notify_one();
if (!success) return;
for (WorkerState state = WorkerState::RUNNING; state != WorkerState::STOPPED;) {
bool needToNotify = false;
if (state != WorkerState::PAUSED ? static_cast<Impl*>(this)->workerCycle()
: (sched_yield(), true)) {
//
// Pause and resume are synchronous. One worker cycle must complete
// before the worker indicates a state change. This is how 'mWorkerState' and
// 'state' interact:
//
// mWorkerState == RUNNING
// client sets mWorkerState := PAUSE_REQUESTED
// last workerCycle gets executed, state := mWorkerState := PAUSED by us
// (or the workers enters the 'error' state if workerCycle fails)
// client gets notified about state change in any case
// thread is doing a busy wait while 'state == PAUSED'
// client sets mWorkerState := RESUME_REQUESTED
// state := mWorkerState (RESUME_REQUESTED)
// mWorkerState := RUNNING, but we don't notify the client yet
// first workerCycle gets executed, the code below triggers a client notification
// (or if workerCycle fails, worker enters 'error' state and also notifies)
// state := mWorkerState (RUNNING)
if (state == WorkerState::RESUME_REQUESTED) {
needToNotify = true;
}
std::lock_guard<std::mutex> lock(mWorkerLock);
state = mWorkerState;
if (mWorkerState == WorkerState::PAUSE_REQUESTED) {
state = mWorkerState = WorkerState::PAUSED;
needToNotify = true;
} else if (mWorkerState == WorkerState::RESUME_REQUESTED) {
mWorkerState = WorkerState::RUNNING;
}
} else {
std::lock_guard<std::mutex> lock(mWorkerLock);
if (state == WorkerState::RESUME_REQUESTED ||
mWorkerState == WorkerState::PAUSE_REQUESTED) {
needToNotify = true;
}
mWorkerState = WorkerState::ERROR;
state = WorkerState::STOPPED;
}
if (needToNotify) {
mWorkerCv.notify_one();
}
}
}
std::thread mWorker;
std::mutex mWorkerLock;
std::condition_variable mWorkerCv;
WorkerState mWorkerState = WorkerState::STOPPED; // GUARDED_BY(mWorkerLock);
};
|
